1. Field of the Invention
The present invention relates to a magnetic detector using a resistor having hysteresis to detect rotation and movement of a magnetic body.
2. Description of the Related Art
FIG. 16 is a top view showing a magnetoresistive element formed on a silicon substrate to be used for a conventional magnetic detector. FIG. 17 is an electric circuit diagram of the magnetoresistive element in FIG. 16. As shown in FIGS. 16 and 17, a magnetoresistive element M is constituted so as to amplify and generate the voltage difference between middle points (nodes) 5 and 6 by bridge-connecting four same resistors 1 to 4 each other, connecting two faced vertexes to a power supply, Vb and an earth GND respectively, and connecting the middle point (node) 5 between resistors 1 and 4 and the middle point (node) 6 between resistors 2 and 3 to two input terminals of a differential amplifier 9 respectively through resistors 7 and 8.
The resistance value of each of resistors 1 to 4 of a magnetoresistive element M symmetrically changes by using Y axis or X axis as a symmetry axis correspondingly to X-and Y-directional applied magnetic fields as shown in FIG. 18 and shows the same curve unless the magnetoresistive element M has hysteresis to a magnetic field change. However, in the case of a magnetoresistive element having hysteresis to a magnetic field change, the resistance value changes depending on the magnetic-field applied direction as shown in FIG. 19.
The magnetic circuit of a conventional magnetic detector using the above magnetoresistive element generally comprises the magnetoresistive element M, magnetic object to be detected 10, and magnet 11 as shown in FIG. 20. In this case, it is assumed that a conventional magnetic detector detects the irregularity of a rotator serving as the magnetic object to be detected 10. That is, the magnetic object to be detected 10 comprises a rotator having a concave 10a and a convex 10b at the outer periphery and the magnet 11 is set so as to face the concave 10a and convex 10b at the outer periphery of the rotator 10. A magnetoresistive element M is set between the rotator 10 and the magnet 11.
When the rotator 10 rotates, the magnetic flux density passing through the magnetoresistive element M changes nearby the boundary between the convex 10a and concave 10b, that is, the edge of the convex 10a if the convex 10a of the rotator 10 approaches the magnet 11 and the resistance values of the resistors 1 and 3 at the side A of the magnetoresistive element M increase and the resistance values of the resistors 2 and 4 at the side B of the magnetoresistive element M increase. Therefore, the differential output waveform of a magnetoresistive element M having no hysteresis becomes the waveform shown in FIG. 21 and waveforms corresponding to the concave 10a and convex 10b become same. Therefore, there is a problem that it is impossible to detect the concave and convex 10a and 10b of the rotator 10.
Moreover, a magnetoresistive element M having hysteresis generates a signal corresponding to the size (distance) D of a gap between the rotator 10 and the magnetoresistive element M while the element M rotates in a constant direction. However, if the rotational direction of the rotator 10 is reversed, there is a problem that a signal level is inverted as shown in FIG. 22.
Furthermore, in the case of the above conventional magnetic circuit, the resistance change value of a magnetoresistive element M decreases at a high temperature. Therefore, as shown in FIG. 23, there is a problem that a signal obtained through rotation of the rotator 10 serving as an object to be detected and the signal accuracy has temperature dependency.
Therefore, to solve the problems of the above conventional example, it is an object of the present invention to provide a magnetic detector capable of obtaining a signal corresponding to the size of the gap between a magnetic object to be detected and a resistor without depending on the moving direction or moving speed of a magnetic object to be detected.
It is another object of the present invention to provide a magnetic detector capable of decreasing the temperature dependency of an output signal (amplitude) of a magnetoresistive element.